I've had the feeling that sentinal SP is tied to the SP your Gladiator/Conjurer/Thaumaturge gets, regardless of what rank it is.. Maybe this is common knowledge, but after some (really limited) testing this seems to be the case. I also asked a friend who said it was so..
So for example, you could take Conjurer to 40, Thaumaturge to 40, and get Sentinel rank 50 in the process. Just looking for other thoughts/confirmations/etc - some in my LS are a little paranoid that SE will change how we get shield skill.. So even though I may never use a shield, I'm considering the above (CON and THM to 40) to knock it out just in case. I think picking up things like Roaming Soul (CON 30) and Siphon TP (THM 32) make this idea more attractive. Raise/Reraise can't hurt, either. Is anyone else looking into this?